1. Field of the Invention
This invention relates to stents that are implantable into body vessels or body cavities, and, more particularly, to such stents that are capable of controllably delivering doses of medicinal substances (e.g., pharmacological agents or drugs).
2. Discussion of the Related Art
Although we discuss below the specific problems associated with medical stents implanted in blood vessels, much of the discussion is applicable to stents implanted in other fluid-carrying vessels of the body.
Coronary artery disease, which is characterized by plaque build up and consequent narrowing of the artery (stenosis), is commonly treated by inserting implantable medical stents into the diseased portion of the artery to prevent it from becoming blocked. The solution is imperfect. One problem is that scar tissue can grow around the stent and block the artery. To reduce the formation of scar tissue some stents are coated or impregnated with a drug, which is passively eluded to inhibit tissue growth.
This type of drug-eluding stent has several disadvantages. First, passively eluding stents do not adequately inhibit the formation of scar tissue and may even produce blood clotting events. Second, the drug delivery mechanism is inflexible; i.e., it is predetermined by the mechanical attributes of the stent and the chemistry of the drug and its binding agents. No provision is made for controlled delivery of multiple doses and/or multiple drugs. Third, while a drug-eluding stent is typically made of a stainless-steel-like material, its shelf life is determined partly by the integrity of its sterile packaging but primarily by the limited lifetime of the drug component. Expired product must be removed from inventory at considerable expense to the user. This problem is exacerbated by the need to inventory stents having a variety of physical sizes. Fourth, static medical stents do not evolve dynamically as the physiology of the vascular system changes over time, which is problematic because replacing a stent is usually difficult, if not impossible, without surgical intervention.
Thus, there is a need in the art for a stent that is capable of remotely controlled delivery of one or more medicinal substances to a body fluid.
There is also a need in the art for a stent that is capable of remotely controlled delivery of multiple doses of one or more medicinal substances to a body fluid.
There is also a need in the art for a stent whose size can be dynamically and remotely controlled in vivo.